Irrigation management plays a critical role in precision farming and maximizing yield productivity. Insufficient irrigation reduces crop productivity, but excessive irrigation imposes a large burden on the water supply of regions affected by agricultural production, especially those that are drought sensitive. Efficient allocation of water is therefore a matter of high social and environmental importance.
Water allocation can be made more efficient by providing more extensive intra-field knowledge of crop water stress. Typical practice for scheduling irrigation in agricultural fields involves assessing the water stress status of plants in the field using time intensive direct measurements from the plants, and scheduling irrigation when plant water stress exceeds some threshold. One such direct measure of water stress is stem water potential (SWP). The procedure for measuring SWP involves determining the vacuum pressure required to squeeze water out of an incision in a leaf stem. SWP provides an accurate measure of water status for an individual plant, but only a tiny fraction of a large field can be tested in a given day, due to the time and effort involved in making SWP measurements.
Such data can enable growers to irrigate the portions of their field having the greatest need for water, while applying significantly less water to unstressed portions. This stands in contrast to many current irrigation practices, which apply a large amount of water over an entire field, and consequently over-irrigate large sections of unstressed crops. A problem with the conventional method is that growers are able to directly measure water stress on only a small subsample of their fields.
Presently, plant water status measurements are typically made by a skilled agronomist using specialized equipment. Such on-the-ground, direct plant water status measurements are time consuming and labor intensive. Stem water potential (SWP), for example, requires careful application of a dedicated apparatus to a particular leaf stem during a limited range of mid-day hours when measurements are most sensitive to water stress (during the peak of evaporative demand). Even a sizable team of testers, therefore, can take SWP measurements on only a small fraction of trees in orchards whose total tree count can number in the tens of thousands. It is therefore infeasible to obtain SWP values for more than a very small fraction of the total number of trees.
Measurements from thermal long-wave infrared (8 μm to 14 μm) have been studied in academic work for over 30 years, and demonstrated as a potentially powerful tool to determine water stress in crops. However, there has been limited use of aerial thermal imagery for irrigation scheduling in commercial settings. Two shortcomings of the results from existing academic work as applied in commercial settings are 1) academic using thermal imagery are not provided in terms that are familiar to growers, and 2) that proper interpretation of thermal imagery also requires accurate, localized weather data, which typically means expensive in-field weather stations.